A pivotal trial of Keryx Biopharmaceuticals Inc's experimental drug Zerenex showed that it improved levels of serum phosphorus and iron in patients on kidney dialysis, according to results published on Thursday. _0"> The trial involved 441 patients, according to the Journal of the American Society of Nephrology, which published the results. Over the four-week efficacy assessment period, mean serum phosphorus for Zerenex patients dropped by 2.2 milligrams per deciliter compared with placebo patients, the trial showed. Most patients with kidney disease that requires dialysis need chronic treatment with phosphate-binding agents to lower and maintain serum phosphorus at acceptable levels. The study found that, if approved, Zerenex would be the only phosphate binder that also increases iron stores, reducing the need for other drugs to treat anemia. Side effects experienced by patients treated with Zerenex included diarrhea, nausea, vomiting and constipation. Serious adver